In August 2006, the European Commission¿s Joint Research Centre (JRC) was asked by DG Enterprise to conduct experimental work to check the validity and suitability of the testing methods proposed by Basofil for the identification, quantification and characterisation of their new fibre melamine.
Experimental results showed that microscopic analysis can be useful but is not a unique technique for the identification of melamine. Identification should be based on FT-IR possibly combined with Thermo Gravimetric (TG) analysis and solubility properties of the fibre.
The agreed allowance of melamine fibre was experimentally evaluated and the value of 7.00 was established.
The normal pre-treatment was shown to be applicable to the new fibre. Melamine is insoluble with all methods of the Directive 96/73/EC. The correction factors d were generally equal to 1.01, except in the case of method 3 and 10, for which d value was 1.00. Five correction factors d of melamine were confirmed through a ring trial including seventeen laboratories. The inter-laboratory trial results established the value of 1.01 as melamine correction factor for methods 3, 4, 8 and 14. The d value calculated in the ring trial for method 7 was 1.07, however the repeatability and reproducibility limits calculated were very poor and the data could not be considered as being part of a normal distribution. As a consequence, it was decided that method 7 would not be considered applicable to blends containing melamine.
Three methods were proposed by the applicant and tested by the JRC for quantification purposes. For the three methods, solubility properties of melamine and other common fibres, supposed to be found in mixture with melamine, were evaluated, together with the effect of key parameters, such as contact time, temperature and concentration of reagent. The method with sodium hypochloride at 90°C was deemed not applicable due to partial solubility of melamine, which was supposed to be insoluble.
The hot formic acid method was considered adequate and applicable in the case of binary mixtures of melamine with aramid and cotton. It was decided that the contact time could be reduced to one hour. The temperature was proved to have a strong influence on this method and it should be carefully maintained in the range 90 ± 2 °C. The hot sulphuric acid method was judged not adequate.
During the 7th meeting of the European network of national experts on textile labelling, a consensus was reached on the need to validate the new method based on hot formic acid and to confirm the correction factors d for aramid (meta and para) and cotton. The JRC organised the ring trial with the participation of seventeen European laboratories, in accordance with the rules laid down in ISO 5725 (1994). The validation was successful. The precision of the test method, which should be quoted as a percentage by mass, was expressed as repeatability and reproducibility limits. Results were 0.74 % and 1.77 %, respectively. The correction factors d for aramid and cotton were evaluated in the same context and the established values are 1.02 for both fibres.
On the basis of the experimental results and of discussions with representative experts from Member States, the definition agreed and proposed for melamine is: ¿fibre formed of at least 50 % by mass of cross-linked macromolecules made up of melamine derivatives¿.